Methods for producing alpha-keto acid and pyruvic acid

ABSTRACT

An electrode catalyst of the present invention contains an electrically conductive material carrying a metal or a metal oxide, and has an electrical conductivity at 30° C. of 1×10 −13  Scm −1  or more.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 16/978,306, filed on Sep. 4, 2020, now allowed, which is a U.S.national phase application of PCT Patent Application Serial No.PCT/JP2019/008691, filed on Mar. 5, 2019, which itself claims priorityto U.S. Provisional Application No. 62/638,311, filed Mar. 5, 2018,which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to an electrode catalyst, a method forproducing a carrier-supported metal alloy, a method forelectrochemically producing ketones using an electrode catalyst, amethod for producing hydroxycarboxylic acids such as pyruvic acid, and afuel cell.

BACKGROUND OF THE INVENTION

Efficient use of biomass resources composed of carbon derived fromcarbon dioxide in the atmosphere is considered to be an effective way ofreducing consumption of petroleum resources. In recent years, theproduction of bioalcohols such as ethanol and ethylene glycol which areused as fuels and raw materials has been industrialized. In the currentindustrial process, bioethanol is produced by alcoholic fermentationwith enzymes using sugar or the like as a raw material, but this processhas a problem of low carbon yield. On the other hand, a method ofproducing an alcohol by hydrogenation from a carboxylic acid abundantlycontained in biomass has been attracting attention (for example, referto Patent Document 1). Further, if energy can be extracted from thealcohol produced from the biomass as a raw material, a carbon neutralcycle can be realized using alcohol as an energy carrier.

Much research has been conducted on techniques regarding fuel cells forconverting alcohols into carboxylic acids. In particular, Pt-Pd basedcatalysts have been attracting attention as electrode catalysts.

As a methanol oxidation catalyst, an alloy obtained by adding Pd to Pthas been known. A rule of thumb known as Vegard's Law has been known asan index for the structures of alloys. The rule of thumb is that thelattice constant of an alloy is an arithmetic mean of the latticeconstants of component metals. For example, the lattice constant ofPt_(x)Pd_(100-x), a(Pt_((100-n))Pd_(n), 0<n<100), can be expressed bythe following formula (1).

a(Pt _((100-n)) Pd _(n))=a(Pt)×((100-n)/100)+a(Pd)×(n/100)   (1)

A method for producing Pt-Pd/C nanoparticles by a polyol method usingethylene glycol as a solvent and a reducing agent has been known (forexample, refer to Non-Patent Document 1). In this production method,trisodium citrate serving as a complexing agent and a stabilizing agent,electrically conductive carbon black serving as a carrier, and palladiumacetylacetonate [Pd(acac)₂] and platinum acetylacetonate [Pt(acac)₂]were dissolved in ethylene glycol which was also a reducing agent, andthe resulting mixture was heated to reflux at 175° C. for 6 hours tocarry out a reduction reaction. After the completion of the reaction,the product is cooled to room temperature and then washed, and dried at75° C. for 12 hours to produce a sample. Pt-Pd in the obtained sample isin the form of nanoparticles having a diameter of about 4.7 nm to 5.2nm. The nanoparticles have larger lattice constants obtained from thepowder XRD pattern than those estimated from Vegard's law.

Further, a method for producing Pt₃Pd₁/C and Pt₁Pd₁/C using a carbonsuspension obtained by suspending carbon black pretreated with 1Mhydrochloric acid and 2M nitric acid in ethylene glycol has been known(for example, refer to Non-Patent Document 2). In this productionmethod, carbon black pretreated with aqua regia is suspended in ethyleneglycol to prepare a carbon suspension. While performing ultrasonictreatment, an aqueous solution obtained by dissolving H₂PtCl₆·6H₂O andPdCl₂ is added dropwise to the carbon suspension, and the mixed solutionof the carbon suspension and the above aqueous solution is stirred.Then, an aqueous NaOH solution is added to the above mixed solution toadjust the pH of the mixed solution to 12 to 13. The pH-adjusted mixedsolution is heated at 130° C. for 3 hours to reduce metal ions, therebyobtaining Pt₃Pd₁/C and Pt₁Pd₁/C. The obtained Pt₃Pd₁/C and Pt₁Pd₁/C arewashed with distilled water and dried under reduced pressure at 70° C.for 8 hours when chloride ions are no longer detected in the AgNO₃solution (1 mol/L). The average primary particle size of Pt₃Pd₁/Cobtained from a low resolution transmission electron microscope (TEM)image is 2.8 nm, and the average primary particle size of Pt₁Pd₁/C is3.6 nm. The lattice constant obtained from the powder XRD pattern ofPt₃Pd₁/C is 3.916×10⁻¹⁰ m, and the lattice constant obtained from thepowder XRD pattern of Pt₁Pd₁/C is 3.910×10⁻¹⁰ m. As described above, thelattice constant obtained from the Pt₃Pd₁/C powder XRD pattern and thelattice constant obtained from the Pt₁Pd₁/C powder XRD pattern arelarger than the lattice constants estimated from Vegard's law.

Citation List

Patent Document 1: International Patent Publication No. 2017/154743

Non-Patent Document 1: W. Wang et al., Electrochemistry Communications,10, 1396-1399 (2008)

Non-Patent Document 2: H. Li et al., J. Phys. Chem. C, 111, 5605-5617(2007)

SUMMARY OF THE INVENTION Technical Problem

The present invention has been made in view of the above circumstances,with an object of providing an electrode catalyst having excellentcatalytic activity as an alcohol oxidation catalyst or a lactic acidoxidation catalyst, a fuel cell including an electrode provided with theaforementioned electrode catalyst, a method for producing ketones usingthe aforementioned electrode catalyst, a method for producing pyruvicacid using the aforementioned electrode catalyst, and a method forproducing a carrier-supported metal alloy.

Solution to Problem

The inventors of the present invention have found that: since metalelements are uniformly mixed and reacted and the electron transferbetween Pd atoms and Pt atoms occurs easily, an ideal surface structureand electronic state for activating alcohols are established in thePt-Pd/C nanoparticles having a lattice constant estimated from theVegard's law as described above, thereby, as an alcohol oxidationcatalyst, allowing an oxidation reaction to proceed highly selectively;and also that: the reaction starts at low voltage, to complete thepresent invention.

(1) An electrode catalyst including an electrically conductive materialcarrying a metal or a metal oxide, and having an electrical conductivityat 30° C. of 1×10⁻¹³ Scm⁻¹ or more.

(2) The electrode catalyst according to (1), wherein the aforementionedmetal is a transition metal and the aforementioned metal oxide is atransition metal oxide.

(3) The electrode catalyst according to (1) or (2), wherein theaforementioned metal includes any one metal or two or more alloysselected from the group consisting of Pd, Pt, Au, Ir, Ru, Rh, and Ag.

(4) The electrode catalyst according to any one of (1) to (3), includingany one metal selected from the group consisting of Pd, Pt, Ru, and Iror an alloy containing two or more metals, and having an electricalconductivity at 30° C. of 1×10⁻¹³ Scm⁻¹ or more.

(5) The electrode catalyst according to (3) or (4), wherein theaforementioned Pd and Pt are in a solid solution state.

(6) The electrode catalyst according to (4), wherein the aforementionedalloy follows Vegard's law.

(7) The electrode catalyst according to (3) to (6), wherein an alloyincluding the aforementioned Pt and Pd have a Pt content of 50 atomic %or more of the alloy.

(8) The electrode catalyst according to (3) to (7), wherein theaforementioned alloy has a work function smaller than an arithmetic meanof work functions of the metals.

(9) The electrode catalyst according to any one of (1) to (8), whereinthe aforementioned metal is in a form of a particle having a diameter of500 nm or less.

(10) The electrode catalyst according to (9), wherein the aforementionedmetal is in a form of a particle having a diameter of 10 nm or less.

(11) A method for producing ketones and carboxylic acids, the methodincluding a step of using an alcohol as a raw material and using acatalyst to carry out an electrochemical oxidation reaction of theaforementioned alcohol.

(12) A method for producing ketones and carboxylic acids, wherein theaforementioned catalyst is the electrode catalyst according to (1) to(10).

(13) The method for producing ketones and carboxylic acids according to(11) or (12), wherein the aforementioned alcohol is a secondary alcohol.

(14) The method for producing ketones and carboxylic acids according to(13), wherein the aforementioned secondary alcohol contains a carboxylgroup.

(15) The method for producing ketones and carboxylic acids according to(11) to (14), wherein the aforementioned alcohol is a secondary alcohol,and the secondary alcohol is a hydroxycarboxylic acid that is asubstituent at an α-position of a carboxyl group.

(16) The method for producing ketones and carboxylic acids according to(15), wherein the aforementioned hydroxycarboxylic acid is lactic acidor pyruvic acid.

(17) The method for producing ketones and carboxylic acids according to(11) or (12), wherein the aforementioned alcohol is a primary alcohol.

(18) The method for producing ketones and carboxylic acids according to(17), wherein the aforementioned primary alcohol is a hydroxycarboxylicacid that is a substituent at an α-position of a carboxyl group.

(19) The method for producing ketones and carboxylic acids according to(18), wherein the aforementioned hydroxycarboxylic acid is glycolicacid.

(20) A method for producing a carrier-supported metal alloy, including:

-   -   (a) a step of dissolving one or two metal reagents in a solvent;    -   (b) a step of bringing an electrically conductive material into        contact;    -   (c) a step of reacting the aforementioned metal reagent with the        aforementioned electrically conductive material, and then        reducing a product obtained by the reaction with a metal hydride        reagent; and    -   (d) a step of treating the product reduced by the aforementioned        metal hydride reagent at 20° C. to 500° C. in the presence of        hydrogen.

(21) The method for producing a carrier-supported metal alloy accordingto (20), wherein the aforementioned metal reagent is a Pd reagent, a Ptreagent, and an Ir reagent.

(22) The method for producing a carrier-supported metal alloy accordingto (20) or (21), wherein the aforementioned electrically conductivematerial is activated carbon or a transition metal.

(23) The method for producing a carrier-supported metal alloy accordingto any one of (20) to (22), wherein the aforementioned metal hydridereagent is NaBH₄.

(24) A fuel cell including an anode, a cathode and an electrolyte, thefuel cell that includes an electrode catalyst on a surface or inside ofthe anode, or on the electrolyte side of the anode, and

-   -   directly generates electricity when alcohols are brought into        contact with the aforementioned catalyst and electrochemically        oxidized to produce ketones or carboxylic acids.

(25) The fuel cell according to (24), wherein the aforementionedelectrode catalyst is the electrode catalyst according to (1) to (10).

(26) The fuel cell according to (24) or (25), wherein an alcohol isbrought into contact with the aforementioned electrode catalyst andoxidized to produce a carboxylic acid in the aforementioned anode.

(27) An energy recovery system for recovering surplus electric powerenergy, the system including: (a) a container for storing carboxylicacids; (b) a means for reducing carboxylic acids to alcohols usingsurplus electric power; (c) a means for storing the obtained alcohols;and (d) a means for oxidizing the aforementioned alcohols to produce theaforementioned carboxylic acids and generating electric power.

Advantageous Effects of the Invention

According to the present invention, it is possible to provide anelectrode catalyst having excellent catalytic activity as an alcoholoxidation catalyst or a lactic acid oxidation catalyst, a fuel cellincluding an electrode provided with the aforementioned electrodecatalyst, a method for producing ketones using the aforementionedelectrode catalyst, a method for producing pyruvic acid using theaforementioned electrode catalyst, and a method for producing acarrier-supported metal alloy. Further, according to the presentinvention, a cycle of producing an alcohol from a carboxylic acid andproducing a carboxylic acid from an alcohol becomes possible.Furthermore, according to the present invention, an alloy followingVegard's law can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a schematic configuration of afuel cell according to the present invention.

FIG. 2 is a diagram showing an XRD pattern of a carbon-supportedplatinum-palladium alloy nanoparticle catalyst.

FIG. 3 is a diagram in which a lattice constant is plotted against acomposition ratio of the carbon-supported platinum-palladium alloynanoparticle catalyst.

FIG. 4 is a diagram showing a transmission electron microscope image anda particle size distribution of a Pt/C catalyst of Example 5.

FIG. 5 is a diagram showing a transmission electron microscope image anda particle size distribution of a Pt₈₀Pd₂₀/C catalyst of Example 2.

FIG. 6 is a diagram showing a transmission electron microscope image anda particle size distribution of a Pt₇₅Pd₂₅/C catalyst of Example 1.

FIG. 7 is a diagram showing a transmission electron microscope image anda particle size distribution of a Pt₅₀Pd₅₀/C catalyst of Example 3.

FIG. 8 is a diagram showing a transmission electron microscope image anda particle size distribution of a Pt₂₅Pd₇₅/C catalyst of Example 4.

FIG. 9 is a diagram showing a transmission electron microscope image anda particle size distribution of a Pd/C catalyst of Example 6.

FIG. 10 is a diagram showing a result of STEM-EDS regardingcarbon-supported platinum-palladium alloy nanoparticles of Example 2.

FIG. 11 is a diagram showing the result of STEM-EDS regarding thecarbon-supported platinum-palladium alloy nanoparticles of Example 2,and is a diagram showing a result of performing a line scan in an arrowportion in FIG. 10 .

FIG. 12 is a diagram showing a result of STEM-EDS regardingcarbon-supported platinum-palladium alloy nanoparticles of Example 1.

FIG. 13 is a diagram showing the result of STEM-EDS regarding thecarbon-supported platinum-palladium alloy nanoparticles of Example 1,and is a diagram showing a result of performing a line scan in an arrowportion in FIG. 12 .

FIG. 14 is a diagram showing a result of STEM-EDS regardingcarbon-supported platinum-palladium alloy nanoparticles of Example 3.

FIG. 15 is a diagram showing the result of STEM-EDS regarding thecarbon-supported platinum-palladium alloy nanoparticles of Example 3,and is a diagram showing a result of performing a line scan in an arrowportion in FIG. 14 .

FIG. 16 is a diagram showing a result of STEM-EDS regardingcarbon-supported platinum-palladium alloy nanoparticles of Example 4.

FIG. 17 is a diagram showing the result of STEM-EDS regarding thecarbon-supported platinum-palladium alloy nanoparticles of Example 4,and is a diagram showing a result of performing a line scan in an arrowportion in FIG. 16 .

FIG. 18 is an optical photograph showing a method of fixing acarbon-supported platinum-palladium alloy nanoparticle catalyst to asample holder in the analysis by X-ray photoelectron spectroscopy.

FIG. 19 is a diagram showing XPS spectra of electrons in the 4f_(7/2)orbital and 4f_(5/2) orbital of Pt.

FIG. 20 is a diagram showing XPS spectra of electrons in the 3d_(5/2)orbital and 3d_(3/2) orbital of Pd.

FIG. 21 is a diagram showing a result of analysis of XPS spectra ofelectrons in the 4f_(7/2) orbital and 4f_(5/2) orbital of Pt.

FIG. 22 is a diagram showing a result of analysis of XPS spectra ofelectrons in the 3d_(5/2) orbital and 3d_(3/2) orbital of Pd.

FIG. 23 is a diagram showing a work function obtained by analyzing a UPSspectrum measured by applying a bias of −0.6 V to a sample.

FIG. 24 is a diagram showing a relationship between the work functionand the onset potential.

FIG. 25 is a schematic configuration diagram showing an electrochemicalcell used for a CV measurement.

FIG. 26 is a schematic configuration diagram showing an electrochemicalcell used for the CV measurement.

FIG. 27 is a diagram showing a result of the second cycle in a CVmeasurement on a Pt/C catalyst.

FIG. 28 is a diagram showing a result of the second cycle in a CVmeasurement in working electrodes containing the carbon-supportedplatinum-palladium alloy nanoparticle catalysts of Examples 1 to 6.

FIG. 29 is a schematic configuration diagram showing an electrochemicalcell used for a CA measurement.

FIG. 30 is a diagram showing the time variation of the current densitydue to CA at each electrical potential in a Pt₈₀Pd₂₀/C catalyst,Pt₇₅Pd₂₅/C catalyst, and Pt₅₀Pd₅₀/C catalyst.

FIG. 31 is a diagram showing the time variation of the current densitydue to CA at each electrical potential in the Pt₈₀Pd₂₀/C catalyst,Pt₇₅Pd₂₅/C catalyst, and Pt₅₀Pd₅₀/C catalyst.

FIG. 32 is a diagram showing the time variation of the current densitydue to CA at each electrical potential in the Pt₈₀Pd₂₀/C catalyst,Pt₇₅Pd₂₅/C catalyst, and Pt₅₀Pd₅₀/C catalyst.

FIG. 33 is a diagram showing the calculated Pt⁰ ratio and the reactiononset potential by analyzing the XPS measurement results of thecarbon-supported platinum-palladium alloy nanoparticle catalystrepresented by the general formula Pt_((100-n))Pd_(n)/C.

FIG. 34 is a schematic diagram showing a crystal structure of acarbon-supported platinum-palladium alloy nanoparticle catalystrepresented by the general formula Pt_((100-n))Pd_(n)/C.

DESCRIPTION OF EMBODIMENTS

Embodiments of the electrode catalyst, the fuel cell, the method forproducing ketones, the method for producing pyruvic acid, and the methodfor producing a carrier-supported metal alloy of the present inventionwill be described.

It should be noted that the present embodiment is specifically describedfor better understanding of the scope and gist of the invention, anddoes not limit the present invention unless otherwise specified.

Electrode Catalyst

An electrode catalyst of the present embodiment contains an electricallyconductive material carrying a metal or a metal oxide, and has anelectrical conductivity at 30° C. of 1×10⁻¹³ Scm⁻¹ or more.

The electrical conductivity of the electrode catalyst of the presentembodiment at 30° C. is 1×10⁻¹³ Scm⁻¹ or more, and preferably 1 Scm⁻¹ ormore. The upper limit of the electrical conductivity may be 7×10⁷ Scm⁻¹or less, or may be 6×10² Scm⁻¹ or less.

If the electrical conductivity at 30° C. is less than 1×10⁻¹³ Scm⁻¹, theelectrons flowing from the circuit do not reach substrate molecules andthe reaction does not start.

As the method for measuring the electrical conductivity of the catalyst,an AC impedance method and the like can be mentioned.

Examples of the metal include transition metals and typical metalelements, and transition metals are preferable from the viewpoint offorming a chemical bond having a strength suitable for reaction with asubstrate molecule.

Examples of the metal oxide include transition metal oxides and metaloxides of typical elements, and transition metal oxides are preferablefrom the viewpoints of efficiency of the reaction activation andchemical stability.

Examples of the transition metal include scandium (Sc), titanium (Ti),vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co),nickel (Ni), copper (Cu), yttrium (Y), zirconium (Zr), niobium (Nb),molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh),palladium (Pd), silver (Ag), lanthanum (La), cerium (Ce), praseodymium(Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),gadolinium (Gd), terpium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), hafnium (Hf),tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir),platinum (Pt) and gold (Au).

Examples of the transition metal oxide include oxides of the abovetransition metals.

Examples of the typical metal element include lithium (Li), sodium (Na),potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium(Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium(Ra), zinc (Zn), cadmium (Cd), mercury (Hg), copernicium (Cn), aluminum(Al), gallium (Ga), indium (In), thallium (Tl), ununtrium (Unt),germanium (Ge), tin (Sn), lead (Pb), freropium (Fl), antimony (Sb),bismuth (Bi), ununpentium (Unp), polonium (Po) and livermolium (Lv).

Examples of the metal oxides of typical elements include oxides of theabove typical metal elements.

The electrically conductive material used in the electrode catalyst ofthe present embodiment is a carrier for the catalyst and has animportant function as an electrode because it is responsible forelectrical conductivity. Examples of such electrically conductivematerials include activated carbon and transition metals.

The electrode catalyst of the present embodiment preferably contains anyone or two or more types of metals selected from the group consisting ofPd, Pt, Au, Ir, Ru, Rh, and Ag. It should be noted that the electrodecatalyst of the present embodiment may contain an oxide of the abovemetals.

By containing any one or two or more types of metals selected from thegroup consisting of Pd, Pt, Au, Ir, Ru, Rh, and Ag, the catalyticactivity is improved in the production of a ketone or pyruvic acid, ascompared with the case of containing other metals.

The electrode catalyst of the present embodiment preferably contains analloy containing any one or two or more types selected from the groupconsisting of Pd, Pt, Ru and Ir. It should be noted that in theelectrode catalyst of the present embodiment, the above alloy mayinclude an oxide of the above metal.

When the electrode catalyst contains an alloy containing any one or twoor more types selected from the group consisting of Pd, Pt, Ru, and Ir,the catalytic activity is improved in the production of a ketone orpyruvic acid, as compared with the case of containing other metals.

The electrode catalyst of the present embodiment preferably has anelectrical conductivity at 30° C. of 1×10⁻¹³ Scm⁻¹ or more whencontaining an alloy containing any one or two or more types selectedfrom the group consisting of Pd, Pt, Ru, and Ir. Further, it ispreferable that the alloy described above follows the Vegard's law. Thatis, it is preferable that in the alloy constituting the electrodecatalyst of the present embodiment, there is an approximatelyproportional relationship between the lattice constant of the alloy andthe concentration of the compositional element. For example, when thealloy is composed of Pd and Pt, the alloy is represented by the generalformula Pt_(x)Pd_(100-x) (0<x<100). The lattice constant ofPt_(x)Pd_(100-x), a(Pt_((100-n))Pd_(n), 0<n<100), can be expressed bythe following formula (1).

a(Pt _((100-n)) Pd _(n))=a(Pt)×((100-n)/100)+a(Pd)×(n/100)   (1)

If the alloy constituting the electrode catalyst of the presentembodiment follows the Vegard's law, it is more excellent in catalyticactivity in the production of a ketone or pyruvic acid than in the caseof not following the Vegard's law. Furthermore, when the alloy followsVegard's law, in terms of the work function of the alloy, it ispreferable that the alloy exhibits a work function smaller than thearithmetic mean of the work functions of the component metalsconstituting the alloy.

A method to examine that the electrode catalyst follows Vegard's law isas follows.

An accurate lattice constant of the alloy can be obtained by analysisusing the Rietveld method by measuring a powder X-ray diffractionpattern of an electrode catalyst with a high signal noise (S/N) ratiousing radiated light having a strong line intensity. Although adiffraction pattern can be obtained using a commercially availabledevice equipped with a tube, a lattice constant may not be obtained insome cases because a pattern with a low S/N ratio is obtained. Inaddition, the lattice constant can be obtained by analyzing single ormultiple diffraction peaks using the Le Bail method, but the accuracymay be lacking in some cases.

In the present embodiment, the catalyst performs an electrochemicaloxidation reaction, but since the present embodiment uses surpluselectric power, it is required to start the reaction at a potential aslow as possible. For that purpose, at this time, electrons need to beprovided to the oxidation reaction from a catalytic metal to which anelectrical potential is applied. The easiness of provision thereofdepends on the relationship between the work function of the alloy andthe reactivity of the reaction substrate, but in the study of thepresent embodiment, the catalytic reaction can be started at an evenlower potential by the catalyst becoming a solid solution. In the caseof Pt and Pd, the ratio of this type of alloy is preferably such thatthe alloy composed of Pt and Pd has a Pt content of 50 atomic % or moreof the alloy. In the case of such a ratio, the reaction can be startedat an even lower potential. Furthermore, at that time, a feature wasfound in that the work function of the alloy was lower than thearithmetic mean of those of both component elements.

Although several methods for obtaining the work function are known,since the alloy on the catalyst carrier is in the form of nanoparticles,a high-resolution method is necessary for the measurement. In thepresent embodiment, the measurement was performed using ultravioletphotoelectron spectroscopy (UPS). The principle of photoelectronspectroscopy is the same as that of XPS. Ultraviolet rays used in UPShave lower energy and narrower energy width than those used in XPS.Therefore, the surface state can be examined with higher resolution thanXPS. In addition, UPS can measure work function (φ) which is energyrequired for extracting an electron from a material.

For metals and semiconductors, the work function is obtained by thefollowing equation using the energy hv of the irradiation light and theenergy width W of the UPS spectrum.

φ=hv−W

hv is the energy of the irradiated ultraviolet ray, which is 21.1 eV forthe HeI line. Further, the energy width W of the UPS spectrum isobtained from the energy at the rising position of the valence band andthe energy at the rising position on the high binding energy side. Theenergy at the rising position of the valence band and the energy at therising position on the high binding energy side can be obtained byextrapolating the UPS spectrum with a straight line and determining anintersection with the background.

The method for measuring the contents of Pd and Pt in the electrodecatalyst is as follows.

They can be examined by measurement by an inductively coupled plasmamethod such as ICP-AES or ICP-MS, or energy dispersive X-ray analysis(EDS) measurement combined with a scanning transmission electronmicroscope (STEM).

When the electrode catalyst of the present embodiment contains Pd and Ptor is an alloy containing Pd and Pt, it is preferable that Pd and Pt arein solid solution states.

When Pd and Pt are in solid solution states, a surface structureadvantageous for activating the substrate molecule and a favorableelectronic state for promoting alcohol oxidation due to electrontransfer between Pd and Pt are formed.

The method for confirming that Pd and Pt are in solid solution states isas follows.

By the element distribution measurement using a scanning transmissionelectron microscope (STEM) and an energy dispersive X-ray analyzer(EDS), it is possible to roughly observe the mixed state of constituentelements. Furthermore, confirmation as a sufficiently mixed solidsolution is possible if it is confirmed that the lattice constantobtained from the powder XRD diffraction satisfies Vegard's law.

The electrode catalyst of the present embodiment may include, as anelectrode carrier, an electrically conductive material for supplyingelectricity from an external circuit to the electrode catalyst, inaddition to the above metals and metal oxides. Examples of theelectrically conductive material include metals, oxides and carbonmaterials. Carbon (C) may be contained as a general and inexpensiveelectrically conductive material. When the electrode catalyst of thepresent embodiment contains carbon (C), for example, a carbon-supportedplatinum-palladium alloy nanoparticle catalyst represented by thegeneral formula Pt_(x)Pd_(100-x)/C (0<x<100) is preferable.

The shape of the electrode catalyst of the present embodiment may be anyshape such as a spherical shape, needle-like shape and plate shape, butit is desirable that the specific surface area of the electrode catalystis large from the viewpoint of maximizing the number of active sites.The size of a particle is defined as the longest diameter of the cutsurface when the particle is cut.

The electrode catalyst of the present embodiment is preferably particleshaving a diameter of 500 nm or less, more preferably particles having adiameter of 50 nm or less, and still more preferably particles having adiameter of 5 nm or less. The electrode catalyst of the presentembodiment may be particles having a diameter of 0.5 nm or more, andpreferably may be particles having a diameter of 1.5 nm or more.

When the electrode catalyst is particles having a diameter of 50 nm orless, since the specific surface area of the catalyst becomes large, thecontact area between the electrode catalyst and the target materialbecomes large, and the catalytic activity improves. Further, when theelectrode catalyst is particles having a diameter of 5 nm or less, morepreferably 5 nm or less, since the specific surface area of theelectrode catalyst becomes larger, the contact area between theelectrode catalyst and the target material becomes larger, and thecatalytic activity further improves.

The diameter of the electrode catalyst of the present embodiment can becalculated by measuring the diameters of the catalyst particles in a TEMimage measured using a transmission electron microscope and subjectingthem to statistical processing.

The electrode catalyst of the present embodiment is composed of a metalor a metal oxide and has an electrical conductivity of 1×10⁻¹³ Scm⁻¹ at30° C. or more, and therefore has an excellent catalytic activity as analcohol oxidation catalyst or a lactic acid oxidation catalyst.

Method for Producing Carrier-supported Metal Alloy

The electrode catalyst of the present invention can be produced by thefollowing method. That is,

-   -   a method for producing a carrier-supported metal alloy,        including:    -   (a) a step of dissolving one or two metal reagents in a solvent;    -   (b) a step of bringing an electrically conductive material into        contact;    -   (c) a step of reacting the aforementioned metal reagent with the        aforementioned electrically conductive material, and then        reducing a product obtained by the reaction with a metal hydride        reagent; and    -   (d) a step of treating a compound of the above step (b) at        20° C. to 500° C. in the presence of hydrogen.

The metal reagent preferably contains any one or two or more typesselected from the group consisting of a Pd reagent, a Pt reagent, a Rureagent and an Ir reagent. These reagents are preferably reagents thatare uniformly soluble in a reaction liquid such as water or an organicsolvent.

When the metal reagent contains any one or two or more types selectedfrom the group consisting of a Pd reagent, a Pt reagent, a Ru reagentand an Ir reagent, it is possible to oxidize substrate molecules moreefficiently than the case of containing other reagents.

The electrically conductive material may be introduced as a precursor ormay be used as carrier particles. More specifically, activated carbonand transition metals are preferable.

By using activated carbon or a transition metal as the electricallyconductive material, electrons generated by an oxidation reaction on thecatalyst can be efficiently circulated to the external circuit.

In the present invention, the above metal reagent, carrier or carrierprecursor is added to water or an organic solvent to react in a uniformstate.

As a metal ion reducing agent, it is appropriate to use a compoundhaving a standard reduction potential that is more negative than that ofhydrogen (0 eV) at room temperature, from the viewpoint of its strongcapacity to reduce transition metal ions to metals. Examples of suchreducing agents include MBH₄, MEt₃BH (M=Na, K), sodium cyanoborohydride(NaBH₃CN), lithium borohydride (LiBH₄), lithium triethylborohydride(LiBHEt₃), borane complexes (BH₃·L), triethylsilane (Et₃SiH) and sodiumbis(2-methoxyethoxy)aluminum hydride (Red-Al). However, it requirescareful attention because some of these reducing agents cannot be usedin an aqueous solution, as they explosively react with water and aretherefore dangerous. In that case, it is appropriate to use a solventother than water (for example, an aprotic polar solvent such astetrahydrofuran, N,N-dimethylformamide and dimethyl sulfoxide) as thesolvent. Of these, NaBH₄ is preferable as the reducing agent because itis water-soluble and easy to handle.

The resultant is further subjected to a reduction treatment at hightemperature in hydrogen gas. The treatment is usually carried out at atemperature of 20° C. to 500° C., and preferably 80° C. to 250° C. It ispreferable to carry out the treatment within this temperature range fromthe viewpoints of sufficiently performing the reduction treatment andsatisfactorily transforming the component metals into solid solutions.Further, the treatment time is usually from 0.1 to 12 hours, andpreferably from 1 to 3 hours. Performing the reduction treatment withinthis time range is preferable in that the reduction treatment can besufficiently performed in a short period of time. Further, the reactionis carried out under hydrogen flow, and 99.99% industrial hydrogen gasis used as hydrogen gas. Industrial hydrogen gas is preferable becauseit can sufficiently reduce the metal.

A method for producing the electrode catalyst of the present embodimentwill be described.

Here, as an example of the method for producing the electrode catalystof the present embodiment, a method for producing the carbon-supportedplatinum-palladium alloy nanoparticle catalyst represented by thegeneral formula Pt_(x)Pd_(100-x)/C (0<x<100) will be described.

A predetermined amount of 2-ethoxyethanol, hexachloroplatinic (IV) acid(H₂PtCl₆) aqueous solution, palladium (II) acetate (Pd(OAc)₂) andacetone were introduced into a test tube, and H₂PtCl₆ and Pd(OAc)₂ aredissolved in the solution by ultrasonication.

Next, a predetermined amount of carbon black is added to the obtainedsolution, and the contents are thoroughly mixed by ultrasonication.

Then, the mixture is stirred while bubbling argon or nitrogen (N₂) gas.

After a predetermined time has passed, the argon or nitrogen (N₂)bubbling is changed to flowing, and a solution obtained by dissolvingsodium borohydride in water is added dropwise little by little with aPasteur pipette. At this time, the liquid temperature is kept constant.

In order to allow the reaction to proceed sufficiently, the temperatureis raised to a predetermined temperature and kept at that temperaturefor a predetermined time.

Then, the resultant is allowed to cool.

The product is separated from the solution by washing the product fromthe test tube into a centrifuge tube with acetone and centrifuging for apredetermined time.

Furthermore, an operation of adding acetone and centrifuging for apredetermined time is repeated twice.

Then, an operation of adding acetone and water and centrifuging for apredetermined time is repeated twice.

Thereafter, acetone is added, and the product is washed into a flask byultrasonication, subjected to suction filtration using a membranefilter, washed with water and acetone, and vacuum dried for apredetermined time using a desiccator.

After drying, a carbon-supported platinum-palladium alloy nanoparticlecatalyst represented by the general formula Pt_(x)Pd_(100-x)/C (0<x<100)is obtained.

Fuel Cell

A fuel cell of the present embodiment includes the electrode catalyst ofthe present embodiment on the surface or inside of an anode, or on theelectrolyte side of the anode. Further, the fuel cell of the presentembodiment directly generates power when an alcohol is brought intocontact with the electrode catalyst and oxidized to produce a carboxylicacid in the anode.

FIG. 1 is a schematic diagram showing a schematic configuration of thefuel cell of the present embodiment.

As shown in FIG. 1 , a fuel cell 10 of the present embodiment includesan anode 11, a cathode 12, and an electrolyte 13.

The anode 11 and the cathode 12 are arranged so as to face each otherwith the electrolyte 13 in between. Further, the anode 11 and thecathode 12 are electrically connected to each other via a conductingwire 20 and a voltmeter 21.

The anode 11 is also called a fuel electrode.

The anode 11 is mainly composed of a porous electrically conductivesolid, and is provided with the electrode catalyst of the presentembodiment on the surface or inside thereof, or on the electrolyte 13side (the side opposite to the cathode 12 side) of the anode 11. Theanode 11 is provided with an anode catalyst layer (not shown) composedof the electrode catalyst of the present embodiment on the electrolyte13 side.

The cathode 12 is also called an air electrode.

The cathode 12 is mainly composed of a catalyst for reducing oxygen andan electrode.

The electrolyte 13 is a proton conductive membrane such as Nafionexhibiting high proton conductivity.

An example of a power generation method by the fuel cell 10 of thepresent embodiment will be described.

Here, the power generation method by the fuel cell 10 will be describedby exemplifying a case where lactic acid serving as an alcohol isbrought into contact with the catalyst of the present embodiment to beoxidized, thereby generating pyruvic acid which is a carboxylic acid.

As shown in FIG. 1 , when lactic acid (LA) is supplied to the anode 11side, the anode catalyst layer provided on one surface 11 a of the anode11 comes into contact with the lactic acid, whereby the lactic acid isoxidized to produce pyruvic acid (PA). At this time, as shown in thefollowing formula (2), hydrogen is desorbed from lactic acid to generatea hydrogen ion (H⁺) and an electron (e⁻).

H2→2H⁺+2e⁻  (2)

Hydrogen ions (H⁺) move in the electrolyte 13 and reach the cathode 12.Electrons (e⁻) move in the external circuit (the conducting wire 20 andthe voltmeter 21) and reach the cathode 12.

On the other hand, as shown in FIG. 1 , when oxygen (O₂) is supplied tothe cathode 12 side, the cathode 12 comes into contact with the oxygen(O₂), whereby the oxygen is reduced to produce water (H₂O). At thistime, as shown in the following formula (3), hydrogen ions (H⁺) andelectrons (e⁻) bond with oxygen (O₂) to generate water (H₂O).

½O₂+2H⁺+2e⁻→H₂O   (3)

The fuel cell 10 generates power by repeating such a redox reaction.

Since the fuel cell of the present embodiment is provided with theelectrode catalyst of the present embodiment on the surface or inside ofthe anode or on the electrolyte side in the anode, by supplying lacticacid to the anode side, it is possible to generate electricity whenlactic acid is oxidized to synthesize pyruvic acid.

The fuel cell may form a so-called membrane electrode assembly composedof an anode, a cathode, and an electrolyte membrane.

Energy Recovery System

An energy recovery system of the present embodiment is a system thatrecovers energy of surplus electric power by reducing carboxylic acidsto alcohols using surplus electric power and oxidizing alcohols tocarboxylic acids.

The energy recovery system of the present embodiment includes: (a) acontainer for storing carboxylic acids; (b) a means for reducingcarboxylic acids to alcohols using surplus electric power; (c) a meansfor storing the obtained alcohols; and (d) a means for oxidizing theaforementioned alcohols to produce the aforementioned carboxylic acidsand generating electric power.

According to the energy recovery system of the present embodiment, it ispossible to efficiently recover, without wasting, surplus electricpower. For example, alcohols produced by using surplus electric powermay be stored in a tank or the like at that place, or alcohols may beaccumulated as an energy carrier from a single or a plurality offacilities, and they can be used to generate electric power using thefuel cell of the present invention. Further, when they are not used asan energy carrier, it is also possible to implement, in the form of, theproduction of useful materials by making use of low electric power. Itshould be noted that grid power and renewable power (solar powergeneration, wind power generation, hydroelectric power generation,geothermal power generation, biomass power generation, wave powergeneration, and the like) are called the first surplus power, and therecovered power is called the second surplus power.

Method for Producing Ketones and Carboxylic Acids

A method for producing ketones and carboxylic acids of the presentembodiment is a method for synthesizing ketones and carboxylic acids byperforming an electrochemical oxidation reaction of alcohols using theelectrode catalyst of the present embodiment.

The method for oxidizing alcohols using the electrode catalyst of thepresent embodiment is not particularly limited, and examples thereofinclude a method in which the electrode catalyst supported on a basematerial (electrode) is brought into contact with alcohols, as in thefuel cell described above, and a method in which the electrode catalystis brought into contact with alcohols by dispersing the electrodecatalyst in a powder form in alcohols and stirring the resulting mixtureof these.

Examples of the raw material alcohols used in the method for producingketones and carboxylic acids of the present embodiment include α-hydroxyacids such as lactic acid, glycolic acid, 2-amino-2-hydroxyacetic acid,2-hydroxy-3,3-dimethylbutanoic acid, 2-hydroxyvaleric acid,α-hydroxyglutaric acid, 2-hydroxysuccinic acid, phenyllactic acid,imidazole-4-lactic acid, 4-hydroxyphenyllactic acid and2-hydroxy-4-methylvaleric acid.

Among secondary alcohols, alcohols containing a carboxyl group arepreferable. Further, among the secondary alcohols, hydroxycarboxylicacids in which the secondary alcohol is a substituent at the α-positionof the carboxyl group are more preferable.

By using secondary alcohols, ketones can be efficiently synthesized.Further, among secondary alcohols, ketones can be synthesized moreefficiently by using alcohols containing a carboxyl group. Moreover,among secondary alcohols, ketones can be synthesized even moreefficiently by using hydroxycarboxylic acids that are substituents atthe α-position of the carboxyl group.

In the method for producing ketones and carboxylic acids of the presentembodiment, since alcohols are oxidized using the electrode catalyst ofthe present embodiment, ketones and carboxylic acids can be efficientlysynthesized.

A primary alcohol can also be used as the raw material in the presentembodiment. Among primary alcohols, alcohols containing a carboxyl groupare preferable. In particular, a hydroxycarboxylic acid in which theprimary hydroxyl group is a substituent at the α-position of thecarboxyl group is preferable. Examples of such a hydroxycarboxylic acidinclude glycolic acid.

Method for Producing Pyruvic Acid

A method for producing pyruvic acid of the present embodiment is amethod for synthesizing pyruvic acid (CH₃COCOOH) by oxidizing lacticacid (CH₃CH(OH)COOH) using the electrode catalyst of the presentembodiment.

The method for oxidizing lactic acid using the electrode catalyst of thepresent embodiment is not particularly limited, and examples thereofinclude a method in which the electrode catalyst supported on a basematerial (electrode) is brought into contact with lactic acid, as in thefuel cell described above, and a method in which the electrode catalystis brought into contact with lactic acid by dispersing the electrodecatalyst in a powder form in lactic acid and stirring the resultingmixture of these.

In the method for producing pyruvic acid of the present embodiment,since lactic acid is oxidized using the electrode catalyst of thepresent embodiment, pyruvic acid can be efficiently synthesized.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to examples, but the present invention is not limited to thefollowing examples.

Catalyst Preparation

Among the carbon-supported platinum-palladium alloy nanoparticlecatalysts represented by the general formula Pt_((100-n))Pd_(n)/C, thosehaving the respective compositions in which n=0, 20, 25, 50, 75 and 100were synthesized by a reduction precipitation method using a personalorganic synthesizer PPS-2511 manufactured by Tokyo Rikakikai Co., Ltd.

Example 1

30 mL of 2-ethoxyethanol, a 560.78 mmol/L H₂PtCl₆ aqueous solution (114μL, 0.096 mmol), 214.4 mg (0.032 mmol) of Pd(OAc), and 5 mL of acetonewere introduced into a test tube, and H₂PtCl₆ and Pd(OAc)₂ weresufficiently dissolved in the resulting solution by 15 minutes ofultrasonication.

Next, 100.0 mg of VULCAN (registered trademark) XC72R manufactured byCabot Corporation was added to the obtained solution, and the contentswere thoroughly mixed by ultrasonication for 10 minutes.

Then, the resulting mixture was stirred for 30 minutes at a rotationspeed of 1,200 rpm while bubbling argon (Ar) gas.

After 30 minutes, the argon (Ar) bubbling was changed to flowing, and asolution obtained by dissolving 38.3 mg of sodium borohydride (1 mmol)in 25 mL of water was added dropwise with a Pasteur pipette over 15minutes. At this time, the liquid temperature was kept at 15° C.

In order to allow the reaction to proceed sufficiently, the temperaturewas raised to 30° C. at a rate of temperature increase of 3° C./min andkept at 30° C. for 45 minutes.

Then, the resultant was allowed to cool to room temperature (20° C.)over 45 minutes. At this time, a product was generated in the test tube.

The product was separated from the solution by washing the product fromthe test tube into a centrifuge tube with 30 mL of acetone andcentrifuging at 6,500 rpm for 3 minutes.

Furthermore, an operation of adding 30 mL of acetone and centrifuging at6,500 rpm for 3 minutes was repeated twice.

Then, an operation of adding 30 mL of acetone and 5 mL of water andcentrifuging at 6,500 rpm for 3 minutes was repeated twice.

Thereafter, 30 mL of acetone was added, and the product was washed intoa flask by ultrasonication, subjected to suction filtration using amembrane filter H100A 047A (pore size: 1.0 μm, manufactured byADVANTEC), washed three times with water, and three times with acetone,and vacuum dried for 12 hours using a desiccator.

After drying, a carbon-supported platinum-palladium alloy nanoparticlecatalyst having a Pd content of 25 at % (atomic %) and a Pt content of75 at % (atomic %) (hereinafter referred to as “Pt₇₅Pd₂₅/C catalyst”)was obtained.

Hydrogen Reduction Treatment

The carbon-supported platinum-palladium alloy nanoparticle catalyst tobe structurally analyzed was subjected to a hydrogen reduction treatmentin a tube furnace in order to obtain the same state as that when theelectrode was produced.

The carbon-supported platinum palladium alloy nanoparticle catalyst wasplaced in a tube furnace, and nitrogen (N₂) gas was passed through thetube furnace at 100 ppm for 15 minutes at 24.5° C. to replace the insideof the tube furnace with nitrogen (N₂) gas.

Next, hydrogen (H₂) gas was passed through the tube furnace at 100 ppmfor 15 minutes to replace the inside of the tube furnace with hydrogen(H₂) gas.

Subsequently, the flow rate of hydrogen (H₂) gas was changed to 60 ppm,and the temperature was raised from 24.5° C. to 250° C. at a rate oftemperature increase of 3.8° C. min⁻¹, held at 250° C. for 120 minutes,and was then naturally cooled to 24.5° C., thereby performing thehydrogen reduction treatment.

Finally, nitrogen (N₂) gas was passed through the tube furnace at 100ppm for 15 minutes to replace the inside of the tube furnace withnitrogen (N₂) gas, and then the electrode was taken out of the tubefurnace.

The particle size of the obtained Pt₇₅Pd₂₅/C catalyst on a TEM image wasmeasured, which showed a result of 2.0 nm or more and 8.9 nm or less.

High Frequency Inductively Coupled Plasma Emission Spectroscopy(ICP-AES)

The content (% by mass) of Pt₇₅Pd₂₅ and the ratio of Pt and Pd in theobtained Pt₇₅Pd₂₅/C catalyst were measured by high frequency inductivelycoupled plasma emission spectroscopy (ICP-AES).

The metal contained in the Pt₇₅Pd₂₅/C catalyst was quantified by highfrequency inductively coupled plasma emission spectroscopy (inductivelycoupled plasma-atomic emission spectroscopy, ICP-AES) using a ThermoFisher SCIENTIFIC iCAP 6300 instrument.

3 mg of the Pt₇₅Pd₂₅/C catalyst was weighed and placed in a screw tubetogether with 3 mL of nitric acid, 9 mL of hydrochloric acid and astirring bar, and was heated and stirred at 80° C. for 2 hours using ahot stirrer at a rotation speed of 120 rpm to prepare a solutioncontaining the Pt₇₅Pd₂₅/C catalyst.

The obtained solution was filtered using a Minisart (registeredtrademark) RC15 syringe filter manufactured by Sartorius AG, and thefiltered solution (filtrate) was made into a solution of about 10 ppmusing a 100 mL volumetric flask.

A platinum standard solution for atomic absorption spectrometry (1,000ppm) was diluted to prepare platinum solutions of 1 ppm, 10 ppm and 20ppm, and a calibration curve was produced. Further, a nickel standardsolution (1,000 ppm) was diluted to prepare nickel solutions of 1 ppm,10 ppm and 20 ppm, and a calibration curve was produced. In addition, apalladium standard solution (1,000 ppm) was diluted to prepare palladiumsolutions of 1 ppm, 10 ppm and 20 ppm, and a calibration curve wasproduced.

The results are shown in Table 1.

Example 2

The same operation as in Example 1 was performed except that a 352.1mmol/L (291 μL, 0.102 mmol) H₂PtCl₆ aqueous solution was used and 25.75mg (0.0256 mmol) of Pd(OAc) was used in Example 1, to obtain acarbon-supported platinum-palladium alloy nanoparticle catalyst having aPd content of 20 at % (atomic %) and a Pt content of 80 at % (atomic %)(hereinafter referred to as “Pt₈₀Pd₂₀/C catalyst”).

An average particle size of the obtained Pt₈₀Pd₂₀/C catalyst wasmeasured in the same manner as in Example 1, which showed a result of2.6 nm or more and 8.8 nm or less.

The content (% by mass) of Pt₈₀Pd₂₀ and the ratio of Pt and Pd in theobtained Pt₈₀Pd₂₀/C catalyst were measured in the same manner as inExample 1. The results are shown in Table 1.

Example 3

The same operation as in Example 1 was performed except that a 352.1mmol/L (219 μL, 0.064 mmol) H₂PtCl₆ aqueous solution was used and 214.37mg (0.064 mmol) of Pd(OAc) was used in Example 1, to obtain acarbon-supported platinum-palladium alloy nanoparticle catalyst having aPd content of 50 at % (atomic %) and a Pt content of 50 at % (atomic %)(hereinafter referred to as “Pt₅₀Pd₅₀/C catalyst”).

The particle size of the obtained Pt₅₀Pd₅₀/C catalyst was measured inthe same manner as in Example 1, which showed a result of 2.7 nm or moreand 13.5 nm or less.

The content (% by mass) of Pt₅₀Pd₅₀ and the ratio of Pt and Pd in theobtained Pt₅₀Pd₅₀/C catalyst were measured in the same manner as inExample 1. The results are shown in Table 1.

Example 4

The same operation as in Example 1 was performed except that a 352.1mmol/L (90.9 μL, 0.032 mmol) H₂PtCl₆ aqueous solution was used and221.55 mg (0.096 mmol) of Pd(OAc) was used in Example 1, to obtain acarbon-supported platinum-palladium alloy nanoparticle catalyst having aPd content of 75 at % (atomic %) and a Pt content of 25 at % (atomic %)(hereinafter referred to as “Pt₂₅Pd₇₅/C catalyst”).

The particle size of the obtained Pt₂₅Pd₇₅/C catalyst was measured inthe same manner as in Example 1, which showed a result of 2.7 nm or moreand 7.7 nm or less.

The content (% by mass) of Pt₂₅Pd₇₅ and the ratio of Pt and Pd in theobtained Pt₂₅Pd₇₅/C catalyst were measured in the same manner as inExample 1. The results are shown in Table 1.

Example 5

The same operation as in Example 1 was performed except that a 352.1mmol/L (364 μL, 0.128 mmol) H₂PtCl₆ aqueous solution was used andPd(OAc)₂ was not used in Example 1, to obtain a carbon-supportedplatinum-palladium alloy nanoparticle catalyst having a Pd content of 0at % (atomic %) and a Pt content of 100 at % (atomic %) (hereinafterreferred to as “Pt/C catalyst”).

The particle size of the obtained Pt/C catalyst was measured in the samemanner as in Example 1, which showed a result of 2.6 nm or more and 21.2nm or less.

The content (% by mass) of Pt and the ratio of Pt and Pd in the obtainedPt/C catalyst were measured in the same manner as in Example 1. Theresults are shown in Table 1.

Example 6

The same operation as in Example 1 was performed except that 228.74 mg(0.128 mmol) of Pd(OAc) was used and a H₂PtCl₆ aqueous solution was notused in Example 1, to obtain a carbon-supported platinum-palladium alloynanoparticle catalyst having a Pd content of 100 at % (atomic %) and aPt content of 0 at % (atomic %) (hereinafter referred to as “Pd/Ccatalyst”).

The particle size of the obtained Pd/C catalyst was measured in the samemanner as in Example 1, which showed a result of 2.8 nm or more and 10.6nm or less.

The content (% by mass) of Pd and the ratio of Pt and Pd in the obtainedPd/C catalyst were measured in the same manner as in Example 1. Theresults are shown in Table 1.

TABLE 1 Ratio of Content of Pt and Pd Catalyst Pt_((100-n))Pd_(n)[atomic ratio] composition [% by mass] Pt Pd Production Example 5 Pt/C21.1 100 — Production Example 2 Pt₈₀Pd₂₀/C 17.6 81 19 Production Example1 Pt₇₅Pd₂₅/C 13.1 73 27 Production Example 3 Pt₅₀Pd₅₀/C 13.5 50 50Production Example 4 Pt₂₅Pd₇₅/C 12.8 23 77 Production Example 6 Pd/C 9.5— 100

From the results shown in Table 1, it was confirmed that thecarbon-supported platinum-palladium alloy nanoparticle catalysts ofExamples 1 to 6 had almost the same composition ratios as thecomposition ratios of those charged.

Powder X-ray Diffraction (XRD) Measurement

A carbon-supported platinum-palladium alloy nanoparticle catalyst thathad been subjected to a hydrogen reduction treatment was placed, in aboro-silicate capillary having an inner diameter of 0.5 mm manufacturedby WJM-Glas/Muller GmbH, up to a position of about 7 mm inside from anend (opening), and in a state of being installed in a vacuum system anddeaerated, an end portion of the capillary was sealed using a gasburner.

With respect to the capillary containing the carbon-supportedplatinum-palladium alloy nanoparticle catalyst that had been sealed, apowder X-ray diffraction (XRD) pattern was measured using a largesynchrotron radiation facility SPring-8 BL44B2, at a wavelengthλ=0.69035 Å (6.9035×10⁻¹¹ m). The obtained XRD pattern is shown in FIG.2 .

As shown in FIG. 2 , when the obtained XRD pattern was compared with thesimulation result of Pt having an fcc structure (hereinafter, referredto as “Pt sim.”) and the simulation result of Pd having an fcc structure(hereinafter, referred to as “Pd sim.”) calculated using a wavelengthλ=6.9035×10⁻¹¹ m, since the obtained XRD pattern is attributed to thepattern of the fcc structure, it was confirmed that the carbon-supportedplatinum-palladium alloy nanoparticle catalysts of Examples 1 to 6 hadfcc structures, and that diffraction peaks shifted so as to approach thediffraction peak of Pd/C as the composition ratios of Pd increased.

The XRD measurement was performed on platinum black (platinum content:above 98.0%) manufactured by Kanto Chemical Co., Inc. and palladiumblack (powder, palladium content: above 99.95%) manufactured by KojimaChemicals Co., Ltd. as reference samples, in the same manner as in thecase of carbon-supported platinum-palladium alloy nanoparticlecatalysts. Hereinafter, the platinum reference sample will be referredto as “Pt ref.” and the palladium reference sample will be referred toas “Pd ref.”.

The sample was identified by analyzing the obtained XRD pattern usingthe Rietveld method. At this time, with respect to a Debye-Scherreroptical system, the calculation was performed with the peak type PVIIand an LP factor of 90. Table 2 shows the structural parameterscalculated by the Rietveld analysis, and FIG. 3 shows a diagram in whichthe lattice constants are plotted against the composition ratios of thecarbon-supported platinum-palladium alloy nanoparticle catalysts.

TABLE 2 Catalyst Lattice constant composition [×10⁻¹⁰ m] ProductionExample 5 Pt/C 3.92172 Production Example 2 Pt₈₀Pd₂₀/C 3.91415Production Example 1 Pt₇₅Pd₂₅/C 3.90987 Production Example 3 Pt₅₀Pd₅₀/C3.90623 Production Example 4 Pt₂₅Pd₇₅/C 3.89524 Production Example 6Pd/C 3.89041 Pt ref. — 3.91901 Pd ref. — 3.89046

From the results of Table 2, the calculated lattice constants of thePt/C catalyst and the Pd/C catalyst substantially coincided with thelattice constants of Pt ref. and Pd ref. On the other hand, it becameclear that the lattice constant of the carbon-supportedplatinum-palladium alloy nanoparticle catalyst changed linearly with thecomposition ratio. Further, from the results of FIG. 3 , it wasconfirmed that the carbon-supported platinum-palladium alloynanoparticle catalysts followed Vegard's law.

Transmission Electron Microscope (TEM) Observation

Three drops of a solution obtained by dispersing a sample(carbon-supported platinum-palladium alloy nanoparticle catalyst) ofabout one spoonful of microspatula in 3 mL of methanol were addeddropwise onto an ester support membrane U1009 manufactured by EM JapanCo., Ltd. using a Pasteur pipette, and then dried to produce a samplegrid.

A transmission electron microscope (TEM) image of the sample was takenusing a transmission electron microscope (JEM-2100HC manufactured byJEOL Ltd., at 200 kV). Further, diameters of about 150 particles in thetransmission electron microscope image were measured, and the particlesize dispersion and the average particle size were calculated. Theresults are shown in FIGS. 4 to 9 and Table 3. FIG. 4 is a diagramshowing a transmission electron microscope image and a particle sizedistribution of the Pt/C catalyst of Example 5. FIG. 5 is a diagramshowing a transmission electron microscope image and a particle sizedistribution of the Pt₈₀Pd₂₀/C catalyst of Example 2. FIG. 6 is adiagram showing a transmission electron microscope image and a particlesize distribution of the Pt₇₅Pd₂₅/C catalyst of Example 1. FIG. 7 is adiagram showing a transmission electron microscope image and a particlesize distribution of the Pt₅₀Pd₅₀/C catalyst of Example 3. FIG. 8 is adiagram showing a transmission electron microscope image and a particlesize distribution of the Pt₂₅Pd₇₅/C catalyst of Example 4. FIG. 9 is adiagram showing a transmission electron microscope image and a particlesize distribution of the Pd/C catalyst of Example 6. Table 3 shows theaverage particle sizes of the carbon-supported platinum-palladium alloynanoparticles.

TABLE 3 Catalyst Average particle size composition [nm] ProductionExample 5 Pt/C 7.8 ± 2.7 Production Example 2 Pt₈₀Pd₂₀/C 4.3 ± 1.3Production Example 1 Pt₇₅Pd₂₅/C 4.2 ± 1.0 Production Example 3Pt₅₀Pd₅₀/C 3.2 to 5.8 4.5 ± 1.3 Production Example 4 Pt₂₅Pd₇₅/C 3.7 to5.9 4.8 ± 1.1 Production Example 6 Pd/C 3.9 to 6.3 5.1 ± 1.2

Scanning Transmission Electron Microscope (STEM) Observation, EnergyDispersive X-ray Spectroscopy (EDS) Measurement

Three drops of a dispersion liquid obtained by dispersing a sample(carbon-supported platinum-palladium alloy nanoparticle catalyst) ofabout one spoonful of microspatula in 3 mL of methanol were addeddropwise onto a microgrid (NP-C10 STEM Cu100P) manufactured by OkenshojiCo., Ltd. using a Pasteur pipette, and then dried to produce a samplegrid.

A line scan was performed by energy dispersive X-ray spectroscopy usinga scanning transmission electron microscope (JEM-ARM200F manufactured byJEOL Ltd., at 200 kV) (scanning transmission electron microscopy-energydispersive spectroscopy, STEM-EDS). The results are shown in FIGS. 10 to17 . FIGS. 10 and 11 are diagrams showing the results of STEM-EDSregarding the carbon-supported platinum-palladium alloy nanoparticles ofExample 2. FIG. 11 is a diagram showing a result of performing a linescan in an arrow portion in FIG. 10 . FIGS. 12 and 13 are diagramsshowing the results of STEM-EDS regarding the carbon-supportedplatinum-palladium alloy nanoparticles of Example 1. FIG. 13 is adiagram showing a result of performing a line scan in an arrow portionin FIG. 12 . FIGS. 14 and 15 are diagrams showing the results ofSTEM-EDS regarding the carbon-supported platinum-palladium alloynanoparticles of Example 3. FIG. 15 is a diagram showing a result ofperforming a line scan in an arrow portion in FIG. 14 . FIGS. 16 and 17are diagrams showing the results of STEM-EDS regarding thecarbon-supported platinum-palladium alloy nanoparticles of Example 4.FIG. 17 is a diagram showing a result of performing a line scan in anarrow portion in FIG. 16 .

From the results of FIGS. 10 to 17 , it is considered that thecarbon-supported platinum-palladium alloy nanoparticles carbon ofExamples 1 to 4 are alloys in which Pt and Pd are thoroughly mixed,because Pt and Pd are distributed in a similar manner.

X-ray Photoelectron Spectroscopy (XPS)

The constituent elements of samples (carbon-supported platinum-palladiumalloy nanoparticle catalysts) and their electronic states were analyzedby X-ray photoelectron spectroscopy (XPS) using an ULVAC-PHI PHI5000VersaProbe II (AlKα radiation, 1486.6 eV) manufactured by ULVAC-PHI,Inc.

As shown in FIG. 18 , a carbon tape was attached to the sample holder,and the sample was placed on the carbon tape.

After confirming that the sample did not peel off from the carbon tapeand introducing the sample holder into an apparatus chamber, the insideof the apparatus chamber was evacuated to perform XPS measurements.

The obtained XPS spectra were calibrated so that the peak bindingenergies derived from C1s of carbon were 284.5 eV. The measurement wasperformed by targeting the spectrum mainly composed of the electrons ofthe 4f_(7/2) orbital and 4f_(5/2) orbital from which the strongestintensity is obtained, regarding the XPS spectrum derived from Pt ineach sample, and targeting the spectrum mainly composed of the electronsof the 3d_(5/2) orbital and 3d_(3/2) orbital from which the strongestintensity is obtained, regarding the XPS spectrum derived from Pd. Inperforming curve fitting analysis of the obtained spectra, the analysiswas performed using a least squares method by assuming that Pt⁰, Pt²⁺and Pt⁴⁺ components were present in Pt in the sample, and that Pd⁰, Pd²⁺and Pd⁴⁺ components were present in Pd. The results are shown in FIGS.19 to 22 . FIG. 19 is a diagram showing XPS spectra of electrons in the4f_(7/2) orbital and 4f_(5/2) orbital of Pt. FIG. 20 is a diagramshowing XPS spectra of electrons in the 3d_(5/2) orbital and 3d_(3/2)orbital of Pd. FIG. 21 is a diagram showing a result of analysis of XPSspectra of electrons in the 4f_(7/2) orbital and 4f_(5/2) orbital of Pt.FIG. 22 is a diagram showing a result of analysis of XPS spectra ofelectrons in the 3d_(5/2) orbital and 3d_(3/2) orbital of Pd.

Further, Table 4 shows the calculated binding energies of the Pt⁰4f_(7/2) orbital and Pd 3d_(5/2) orbital.

TABLE 4 Binding Binding energy of energy of 4f_(7/2) orbital 3d_(5/2)orbital Catalyst of Pt⁰ of Pd composition [eV] [eV] Production Example 5Pt/C 71.15 — Production Example 2 Pt₈₀Pd₂₀/C 71.20 335.50 ProductionExample 1 Pt₇₅Pd₂₅/C 71.27 335.56 Production Example 3 Pt₅₀Pd₅₀/C 71.21335.45 Production Example 4 Pt₂₅Pd₇₅/C 71.09 335.33 Production Example 6Pd/C — 335.25

From the results of Table 4, it was found that Pt₇₅Pd₂₅/C exhibited themaximum values for the binding energy of the 4f_(7/2) orbital of Pt⁰ andthe binding energy of the 3d_(5/2) orbital of Pd, as compared with theother compositions. From these results, it was confirmed that Pt₇₅Pd₂₅/Chad a stronger electronic interaction between Pt and Pd, as comparedwith the other compositions.

Measurement of XPU

UPS measurements were performed in order to determine the work functionof the catalysts. For the UPS measurement, the measurement was performedusing an electron spectroscopy analyzer (Versa Probe II, ULVAC-PHI) withthe HeI line in a state where a Pd-Pt/C powder sample was placed on ameasurement stage, a gold wire was placed thereon, and a mask wasfurther attached and fixed.

The work function obtained by analyzing the UPS spectrum measured byapplying a bias of −0.6 V to a sample is shown in Table 5 and FIG. 23 .From Table 5 and FIG. 23 , it became clear that the work functions ofPd-Pt/C catalysts varied depending on the composition, and all had awork function smaller than that of Pt.

Table 6 shows the work functions of simple metals.

TABLE 5 Catalyst Work function (eV) Pt/C 5.525 Pt₈₀Pd₂₀/C 5.295Pt₇₅Pd₂₅/C 5.08 Pt₅₀Pd₅₀/C 5.23 Pt₂₅Pd₇₅/C 5.34

TABLE 6 Metal Work function (eV) Ru 4.71 Rh 4.98 Pd 5.12 Ag 4.26 Ir 5.27Pt 5.65 Au 5.1

From Table 6, it can be seen that the work functions of the metals inthe fifth period are larger than those of the metals in the fourthperiod, and even among the metals in the same period, the work functionsof Ag and Au in which electrons at the Fermi level are on the s-orbitalare smaller than those of other metals. Therefore, in the Pd-Pt/Ccatalysts, it is considered that electrons move from Pd having a smallwork function to Pt having a large work function. As a result, since thenuclear charge per electron on Pt (the force with which the atomicnucleus of Pt attracts an electron) decreases as the electron density onPt increases, the work function of the alloy as a whole decreases.Although the amount of charge transfer between Pt and Pd variesdepending on the coordination number of the metal element, the alloystructure, and the stability of the component metals, in the case ofPd-Pt/C catalysts, it is considered that the amount of charge transferreaches a maximum value in the Pt₇₅Pd₂₅/C catalyst and its work functionbecomes a minimum value.

Next, FIG. 24 shows a relationship between the work function of PdPtobtained previously and the onset potential of the electrooxidation oflactic acid. As a result, it was revealed that Pd-Pt/C which has a workfunction smaller than the arithmetic mean of the work functions of Pt/Cand Pd/C shown by the dotted line exhibits high activity for theelectrochemical oxidation of alcohol. It is considered that this isbecause the electrochemical oxidation of alcohol requires stronginteraction between the alcohol (hydroxyl group (—OH)) and the catalyst,so that Pt which strongly interacts with protons exhibits higheractivity than Pd. Furthermore, it is considered that the alloy catalystPt₇₅Pd₂₅/C having a small work function has an ability to donateelectrons to an antibonding orbital of the substrate, and thereforehighly activates the substrate molecule and exhibits high catalyticactivity.

Cyclic Voltammetry (CV) Measurement

FIGS. 25 and 26 are schematic configuration diagrams showing anelectrochemical cell used for a CV measurement.

In FIGS. 25 and 26 , reference numeral 21 denotes a cell, referencenumeral 22 denotes a sealing plug that seals the cell 21, referencenumeral 23 denotes a working electrode, reference numeral 24 denotes athermometer, reference numeral 25 denotes a first gas introduction pipe,reference numeral 26 denotes a stirring bar, reference numeral 27denotes a counter electrode, reference numeral 28 denotes a referenceelectrode, and reference numeral 29 denotes a second gas introductionpipe.

As the working electrode 23, electrodes containing the carbon-supportedplatinum-palladium alloy nanoparticle catalysts of Examples 1 to 6 wereinstalled. As the counter electrode 27, a platinum counter electrode(manufactured by BAS Inc.) having an electrode diameter of 0.5 mm and alength of 23 cm was used. As the reference electrode 28, anAg/AgCl-saturated KCl silver-silver chloride reference electrode(manufactured by Inter Chemical Ltd.) was used. Further, as apotentiostat, VersaSTAT4 manufactured by Princeton Applied Research wasused.

As a blank sample, a 0.2 mol/L sodium sulfate aqueous solution obtainedby dissolving 14.20 g (0.1000 mol) of sodium sulfate in 500 mL ofsuperelectrolyzed water was prepared, and a mixed aqueous solutioncontaining 0.2 mol/L sodium sulfate and 30 mmol/L lactic acid obtainedby dissolving 14.20 g (0.1000 mol) of sodium sulfate and 1.12 mL (15mmol) of lactic acid in superelectrolyzed water so that the total volumewas 500 mL was prepared.

The mixed aqueous solution was introduced into the cell 21 having avolume of 80 mL, and then, while bubbling an inert gas for 30 minutes,heated to a measurement temperature using a hot stirrer equipped withthe stirring bar 26 while stirring at 300 rpm.

After 30 minutes, it was confirmed that the liquid temperature reached70° C., a thermocouple portion part of Digital Fine Thermo DG2Nmanufactured by Hakko Electric Co., Ltd. was removed from the solution,and as shown in FIG. 26 , the inert gas bubbling was switched toflowing.

Each electrode was connected to Versastat 4 manufactured by PrincetonApplied Research, and the CV measurement was performed for 3 cycles at ascan rate of 10 mVs⁻¹ in the range of −100 mV vs RHE to +1,000 mV vsRHE. The results are shown in FIG. 27 . FIG. 27 is a diagram showing theresult of the second cycle in the CV measurement on the Pt/C catalyst.

Regarding the mixed aqueous solution containing 30 mmol/L lactic acid,when the electrical potential was swept from negative to positive orfrom positive to negative, an oxidation peak not found in the blanksample was confirmed near 641 mV vs RHE. It is considered that thechange in the current density when the electrical potential was appliedfrom positive to negative indicated the occurrence of an oxidationreaction of lactic acid. Further, it is presumed that the cause for thedeactivation during the process was a decrease in the reaction rate dueto poisoning of the catalyst surface. Moreover, the oxidation peakconfirmed in the process of sweeping the electrical potential frompositive to negative indicates that this reaction is an irreversiblereaction. It is considered that the reason why the current value ishigher than that in the first half is the occurrence of electrontransfer due to dissociation of the material adsorbed onto the surfaceof the working electrode.

The results of the second cycle in the CV measurement in the workingelectrode containing the carbon-supported platinum-palladium alloynanoparticle catalysts of Examples 1 to 6, which were standardized bythe current density at the peak top generated when the electricalpotential was swept from negative to positive, are shown in FIG. 28 .Since the current density near 400 mV vs RHE was no different from themeasurement result in the blank sample, the intersection between itsextended line and the peak tangent was defined as the reaction onsetpotential. Table 7 shows the reaction onset potentials calculatedtherefrom.

TABLE 7 Catalyst Reaction onset potential composition [mV vs RHE]Production Example 5 Pt/C 527.2 Production Example 2 Pt₈₀Pd₂₀/C 507.5Production Example 1 Pt₇₅Pd₂₅/C 498.8 Production Example 3 Pt₅₀Pd₅₀/C512.6 Production Example 4 Pt₂₅Pd₇₅/C 605.4 Production Example 6 Pd/C814.2

From the results of Table 7, it was found that among thecarbon-supported platinum-palladium alloy nanoparticle catalysts ofExamples 1 to 6, the Pt₇₅Pd₂₅/C catalyst exhibited the lowest reactiononset potential.

Controlled Potential Electrolysis (Chronoamperometry (CA)) Measurement

With respect to the Pt/C catalyst, Pt₈₀Pd₂₀/C catalyst, Pt₇₅Pd₂₅/Ccatalyst, and Pt₅₀Pd₅₀/C catalyst whose reaction onset potentials areclose to each other, the production distribution of pyruvic acid wasinvestigated by CA at 650 mV vs RHE, which is near the electricalpotential of the oxidation peak of the Pt/C catalyst, at 550 mV vs RHE,which is near the reaction onset potential of the Pt/C catalyst, and at500 mV vs RHE, which is near the reaction onset potential of thePt₇₅Pd₂₅/C catalyst.

FIG. 29 is a schematic configuration diagram showing an electrochemicalcell used for the CA measurement.

In FIG. 29 , reference numeral 41 denotes a first cell, referencenumeral 42 denotes a second cell, reference numeral 43 denotes a sealingplug that seals the first cell 41, reference numeral 44 denotes asealing plug that seals the second cell 42, reference numeral 45 denotesa working electrode, reference numeral 46 denotes a counter electrode,reference numeral 47 denotes a reference electrode, reference numeral 48denotes a first gas introduction pipe, reference numeral 49 denotes asecond gas introduction pipe, reference numeral 50 denotes a diaphragmprovided in the middle of a connecting portion 51 between the first cell41 and the second cell 42, and reference numerals 52 and 53 denotestirring bars.

As the diaphragm 50, Nafion (registered trademark) NRE-212 manufacturedby Sigma-Aldrich Co. LLC. was used.

As the working electrode 45, electrodes containing the carbon-supportedplatinum-palladium alloy nanoparticle catalysts of Examples 1 to 6 wereinstalled. As the counter electrode 46, a platinum counter electrode(manufactured by BAS Inc.) having an electrode diameter of 0.5 mm and alength of 23 cm was used. As the reference electrode 47, anAg/AgCl-saturated KCl silver-silver chloride reference electrode(manufactured by Inter Chemical Ltd.) was used.

As reaction solutions, 40 mL each of a 0.2 mol/L sodium sulfate aqueoussolution containing 30 mmol/L lactic acid and a 0.2 mol/L sodium sulfateaqueous solution containing no substrate were introduced into the firstcell 41 and the second cell 42, respectively.

Then, while bubbling an inert gas for 30 minutes, the reaction solutionsin the first cell 41 and the second cell 42 were heated to 70° C. usinghot stirrers equipped with the stirring bars 52 and 53, respectively,while stirring at 450 rpm.

After 30 minutes, it was confirmed that the liquid temperature reached70° C., and the inert gas bubbling was switched to flowing.

Each electrode was connected to Versastat 4 manufactured by PrincetonApplied Research, and the CV measurement was performed for 3 cycles at ascan rate of 10 mVs⁻¹ in the range of −100 mV vs RHE to +1,000 mV vsRHE.

Then, an electrical potential of 650 mV vs RHE, 550 mV vs RHE, or 500 mVvs RHE was applied and the reaction was performed at a constantpotential for 2 hours, and the current density was plotted at intervalsof 10 points/s.

Quantification of the product was performed by high performance liquidchromatography (HPLC) using a high performance liquid chromatographProminence manufactured by Shimadzu Corporation. A 50 mmol/L aqueoussolution of perchloric acid was used as a buffer. 500 μL of the reactionsolution was collected in a dedicated vial using a syringe, before thestart of CA measurement, at the time when 1 hour had elapsed, and at thetime of the completion of the reaction (at the time when 2 hours hadelapsed), and the concentration of pyruvic acid was calculated from anarea value of the measurement result of each reaction solution.

FIGS. 30 to 32 show the time variation of the current density due to CAat each electrical potential in the Pt₈₀Pd₂₀/C catalyst, the Pt₇₅Pd₂₅/Ccatalyst, and the Pt₅₀Pd₅₀/C catalyst. Further, Table 8 shows eachelectrical potential, the conversion rate of lactic acid in eachcarbon-supported platinum-palladium alloy nanoparticle catalyst, theproduction rate of pyruvic acid, and the Faradaic efficiency (F. E.) ofpyruvic acid.

It should be noted that the conversion rate of lactic acid refers to theratio of reacted lactic acid in the lactic acid introduced before thereaction, and was calculated by dividing the amount of lactic acidmaterial after the completion of the reaction by the amount of lacticacid material before the start of CA measurement. The production rate ofpyruvic acid refers to the ratio of pyruvic acid formed by the reactionfrom the lactic acid introduced before the reaction, and was calculatedby dividing the amount of pyruvic acid material after the completion ofthe reaction by the amount of pyruvic acid material before the start ofCA measurement. The Faradaic efficiency of pyruvic acid productionrefers to the ratio of the electric current used for the synthesis ofpyruvic acid to the electric current flowing through the circuit, andwas calculated by dividing, the total amount of electrons (mol)generated by the production of pyruvic acid generated which wascalculated by multiplying the amount of pyruvic acid material producedand the number of electrons (2 electrons) generated along with theproduction of one molecule of pyruvic acid, by the total number ofelectrons (mol) flowing through the circuit which was calculated bydividing the total amount of electric charge flowing through the circuitby the Faraday constant (96490 (C/mol)).

TABLE 8 Pyruvic acid Potential Conversion production rate F. E. [mV vsrate [%] [%] [%] RHE] 650 550 500 650 550 500 650 550 500 Pt/C 19 0 0 240 0 114 0 0 Pt₈₀Pd₂₀/C 3 0 0 3 0 0 112 0 0 Pt₇₅Pd₂₅/C 7 10 11 2 11 12112 100 110 Pt₅₀Pd₅₀/C 0 11 8 0 13 8 0 118 108

From the results of FIGS. 30 to 32 and Table 8, it was found that lacticacid was converted to pyruvic acid with a selectivity of 100% in thereaction on the working electrode containing the carbon-supportedplatinum-palladium alloy nanoparticle catalyst. It should be noted thatthe selectivity referred to here is the amount of pyruvic acid materialproduced with respect to the amount of the entire product material whenperforming HPLC on the solution at the time of the completion of thereaction. In the present experiment, among the products, since noproduct other than pyruvic acid was confirmed, the selectivity was 100%.

Although the final production rate of pyruvic acid by the workingelectrode containing the Pt/C catalyst was as high as 24% for 650 mV vsRHE, it was found that the production rate of pyruvic acid was lower, inthe working electrodes containing other carbon-supportedplatinum-palladium alloy nanoparticle catalysts, than that of theworking electrode containing the Pt/C catalyst. It is considered thatthis is because the measurement was made, for the working electrodecontaining the carbon-supported platinum-palladium alloy nanoparticlecatalyst other than the Pt/C catalyst, after the oxidation peakpotential, so that the surface of the working electrode was poisoned andthe reaction rate decreased.

On the other hand, in the measurement at 500 mV vs RHE, which is lowerthan the reaction onset potential of the working electrode containingthe Pt/C catalyst, the reaction did not proceed with the Pt/C catalyst,and the production rate of pyruvic acid with the Pt₇₅Pd₂₅/C catalystwhose reaction onset potential was the lowest was maximized.

From the above results, it became clear that it is possible tosynthesize pyruvic acid from lactic acid with a selectivity of 100% evenat a low electrical potential where the reaction does not proceed withthe platinum catalyst, by using the working electrode containing thecarbon-supported platinum-palladium alloy nanoparticle catalyst otherthan the Pt/C catalyst.

FIG. 33 shows the calculated Pt⁰ ratio and the reaction onset potentialby analyzing the XPS measurement result of the carbon-supported platinumpalladium alloy nanoparticle catalyst represented by the general formulaPt_((100-n))Pd_(n)/C.

From the results of FIG. 33 , it was found that the ratio of Pt⁰ in thePt₇₅Pd₂₅/C catalyst was the highest. It was also found that thePt₇₅Pd₂₅/C catalyst had the lowest reaction onset potential.

From the above results, it is considered that the cause for the highcatalytic activity of the Pt₇₅Pd₂₅/C catalyst is, as shown in FIG. 34 ,the electronic interaction between Pt and Pd being stronger than thoseof the carbon-supported platinum-palladium alloy nanoparticle catalystshaving other composition ratios, and thus the ratio of Pt⁰ increased andthe active sites increased.

Reference Signs List

-   -   10: Fuel cell    -   11: Anode    -   12: Cathode    -   13: Electrolyte    -   20: Conducting wire    -   21: Voltmeter

1-8. (canceled)
 9. A fuel cell comprising an anode, a cathode and anelectrolyte, wherein the anode comprises an electrode catalystcomprising an electrically conductive material carrying a metal or ametal oxide, and having an electrical conductivity at 30° C. of 1×10⁻¹³Scm⁻¹ or more; said metal is one or more transition metals and saidmetal oxide is an oxide of a transition metal; and said electrolyte hasproton conductivity; and wherein an α-hydroxycarboxylic acid contactsthe anode to generate protons and electrons; the protons move in theelectrolyte and reach the cathode; and the protons and oxygen arereacted on the cathode to produce water.
 10. An energy recovery systemfor recovering surplus electric power energy, the system comprising: acontainer for storing an α-keto carboxylic acids; a container forstoring an α-hydroxycarboxylic acid; and a means for electrochemicallyoxidizing said α-hydroxycarboxylic acid to produce saidα-hydroxycarboxylic acid and generating electric power, wherein saidmeans comprise an anode; wherein the anode comprises an electrodecatalyst comprising an electrically conductive material carrying a metalor a metal oxide, and having an electrical conductivity at 30° C. of1×10⁻¹³ Scm⁻¹ or more; said metal is one or more transition metals andsaid metal oxide is an oxide of a transition metal’ and wherein theα-hydroxycarboxylic acid contacts the anode to generate protons andelectrons.
 11. A power generation method for generating electric powerusing the fuel cell of claim 9.